This invention relates to the nitration of chlorobenzene and, more particularly, to a method for controlling the para:ortho isomer distribution of nitrochlorobenzenes by the vapor phase nitration of chlorobenzene in the presence of small pore size molecular sieve catalysts.
Nitrochlorobenzenes are widely used intermediates in organic synthesis including materials for producing dyes, pharmaceuticals and synthetic fibers. The usual methods for making nitrochlorobenzenes are liquid phase reactions employing mixed acids. A sulfuric/nitric acid mixture is the chief industrial nitrating agent. Other mixed acids for nitration of monochlorobenzene are acetic/nitric acid mixtures as described, for example, in U.S. Pat. No. 3,180,900. In U.S. Pat. No. 3,928,476, the latter type nitration is conducted over silica-alumina or alumina supports.
Vapor phase nitration also has been employed heretofore. It has been used for the nitration of paraffins as described by Hass et al. Ind. Eng. Chem. 28 (3), 340-44 (1936), and U.S. Pat. No. 1,967,667; and for the nitration of benzene and toluene as disclosed by McKee and Wilhelm, Ind. Eng. Chem. 28 (6), 662-67 (1936), and U.S. Pat. No. 2,109,873. McKee and Wilhelm catalyzed their reaction with silica gel, with best results being reported by use of 14 mesh material. Bauxite and alumina were reported to be ineffective catalysts in the vapor phase nitration of benzene.
Further background information on conventional nitration methods can be had by reference to Albright and Hanson, "Industrial and Laboratory Nitrations," ACS Symposium Series 22, 1976, American Chemical Society, Washington, D.C.
Although the prior art discloses methods for increasing the proportion of para isomer in nitrochlorobenzene product mixtures from the usual 65% para: 35% ortho distribution, it does not teach convenient means for controlling the isomer distribution within a broad range.